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The cage-like molecule C60 has incarcerated a hefty new prisoner. Methane is the first organic molecule, and the largest of any kind, to be encapsulated in this way (Angew. Chem., Int. Ed. 2019, DOI: 10.1002/anie.201900983). Researchers have previously caged small molecules like H2 and H2O by opening a hole in C60, putting the prisoner inside, and then chemically stitching the entrance closed. But larger occupants need a bigger opening, of a size researchers have previously been unable to close. “It’s not that hard to make holes in C60 and put molecules inside, but actually closing them up is incredibly difficult,” says Richard J. Whitby, the University of Southampton chemist who led the research. His team created a fullerene cage with a relatively large opening—a 17-membered-ring that included a sulfur atom—and forced methane inside at high pressure. Then the researchers oxidized the sulfur and used a photochemical reaction to eject sulfur monoxide, which contracted the ring. Further reactions closed the hole completely, trapping a single methane molecule that could rotate freely in its cage. Isolating molecules inside C60 enables researchers to investigate their quantum properties. X-ray crystallography revealed that the methane’s hydrogen atoms were smeared into a spherical shell, corresponding to their delocalized nuclear wave function. The team now hopes to snare other molecules, including O2 and NH3.